The subject matter of the present invention relates to well testing, and more particularly, to a retrievable centerbody (`choke`) used to facilitate downhole measurement of flowrates of fluid flowing upward in an oil well borehole.
After the borehole of an oilwell has been drilled, a section of pipe is lowered into the borehole, the pipe having certain openings disposed therethrough for receiving formation fluids and causing the fluids to move upward through the pipe. One portion of the pipe is dedicated to measuring the flowrate of the fluid flowing upward through the pipe. This portion of the pipe is constricted in terms of its diameter. As noted in U.S. Pat. No. 4,856,344, a gauge measures the differential pressure of the fluid across the constricted portion of the pipe. The differential pressure is translatable to a flowrate figure. The flowrate figure is translatable to a particular resolution in terms of barrels per day (bbl/day) of fluid, determined by the resolution of the differential pressure gauge. The lowest flowrate that can be measured occurs when the resulting differential pressure through the constriction is equal to the resolution of the pressure gauge. If the differential pressure through the constriction can be increased, or the resolution of the pressure gauge can be increased, then a lower flowrate can be measured. While a smaller constriction would produce the desired increase in delta pressure for a given flowrate, it is deemed necessary not to reduce the pipe bore beyond a certain minimum value. Therefore, an alternative solution to this problem is required in order to provide a accurate measurement of low fluid flowrates.